Object entries in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does Object.entries() do in JavaScript?

Object.entries() takes an object and returns an array of its own enumerable property [key, value] pairs.

Think of it like turning a box of labeled items into a list of label-item pairs.

beginner

How is the output of Object.entries() structured?

The output is an array where each element is a two-item array: the first item is the property key (a string), and the second is the property value.

Example: [['name', 'Alice'], ['age', 30]]

intermediate

Can Object.entries() be used on arrays? What happens?

Yes! Arrays are objects with numeric keys as strings. Object.entries() returns pairs of index and value.

Example: Object.entries(['a', 'b']) returns [['0', 'a'], ['1', 'b']].

intermediate

Does Object.entries() include inherited properties?

No. It only includes the object's own enumerable properties, not those inherited from its prototype.

beginner

How can Object.entries() help in looping over an object?

<p>You can use <code>Object.entries()</code> with <code>for...of</code> to get key and value in each loop step.</p><p>Example:<br><code>for (const [key, value] of Object.entries(obj)) { console.log(key, value); }</code></p>

What does Object.entries({a: 1, b: 2}) return?

A {a: 1, b: 2}

B ['a', 'b']

C [1, 2]

D [['a', 1], ['b', 2]]

Object.entries() returns an array of [key, value] pairs, so the correct answer is [['a', 1], ['b', 2]].

Does Object.entries() include properties from the object's prototype?

A No, only own enumerable properties

B Yes, all properties

C Only non-enumerable properties

D Only properties starting with underscore

Object.entries() only includes the object's own enumerable properties, not inherited ones.

What is the type of each element inside the array returned by Object.entries()?

A Array of two elements

B String

C Number

D Object

Each element is an array with two items: the key and the value.

What will Object.entries(['x', 'y']) return?

A [0, 1]

B [['0', 'x'], ['1', 'y']]

C ['x', 'y']

D []

Arrays are objects with numeric keys as strings, so Object.entries() returns index-value pairs.

Which loop works well with Object.entries() to access keys and values?

A for...in

B while

C for...of

D do...while

for...of loops over iterable objects like arrays, making it perfect for Object.entries() output.

Explain how Object.entries() transforms an object and give a simple example.

Think about turning a labeled box into a list of label-item pairs.

Describe how you can use Object.entries() to loop through an object's properties.

Focus on how to get both key and value easily in a loop.